[R-pkg-team] Bug#912254: Template JS

[Gordon Ball]

On closer inspection, it looks like quite a lot of the javascript
referenced in the pkgdown templates is not packaged, or has unmatched
versions:

package, target, in-debian
jquery, 3.3.1, 3.3.1
bootswatch, 3.3.7, 3.3.7
bootstrap, 3.3.7, 3.4.1
font-awesome, 5.7.1, 4.7.0
clipboard, 2.0.4, unpackaged
headroom, 0.9.4, unpackaged
docsearch, 2.6.1, unpackaged
mark, 8.11.1, unpackaged
mathjax, 2.7.5, 2.7.4

Given that pkgdown primarily advertises itself as generating static HTML
documentation for web use, rather than traditional R man
pages/vignettes, I suspect it isn't worth the time to try and
reconstruct this HTML documentation.

It appears to normally consist of an amalgamation of the README,
changelog, man pages and vignettes into a single set of HTML pages. I
think it's probably enough to provide each of those things separately as
normal for an R package for those users who want to rely on offline
documentation.